1. Field of the Invention
The present invention relates to a spam processing of electronic mails, and more particularly to a mass mail detection system that is suitable when a dealer that manages a large-scale electronic mail server, such as a portable phone or an ISP, detects an annoying mail such as an unapproved advertisement contained in the electronic mails delivered via the electronic mail server, as well as to a mail server provided with the mass mail detection system.
2. Description of the Related Art
In accordance with the spread of electronic mails, there is an increasing number of annoying mails using electronic mail as transfer means, thereby raising a social problem. Conventionally, as means for preventing those annoying mails, a method such as described below has been generally used. Namely, the receiver of electronic mails prepares a mechanism for detecting an annoying mail in the terminal used for receiving the electronic mails, whereby the annoying mails are automatically deleted.
For example, SpamAssassin is a software that uses a rule base system, and bogofilter is a software that uses a mechanical learning method; both of which are used as an effective mechanism mainly among the PC users. Here, these softwares are shown respectively in the following documents 1 and 2.
Document 1:    http://www.au.spamassassin.org/presentations/SAGE_IE—2002/
Document 2:    http://bogofilter.sourceforge.net/bogofilter_man.html
The above-described conventional techniques presuppose that the receiver of electronic mails uses a receiving terminal having an information processing capability of a prescribed level or higher such as a PC, so that they are unsuitable for the receiving terminals having a comparatively low capability such as portable phones. In order to aid receiving terminals having a comparatively low capability such as portable phones, it is desirable that the mail server on the dealer side is provided with means for detecting a mass mail.
However, the above-described conventional techniques have a low processing speed for use in the server, thereby raising a problem in that large-scale equipment is needed. Further, it is difficult to prepare a common detection rule or mechanical learning result of mass mails for a large number of users, and also the cost for maintenance and management in coping with new types of spam has been huge, thereby raising a problem.